Energy reservoirs, in particular rechargeable batteries having a long service life during which they can furnish electrical power, are required in numerous applications. The service life of a battery is limited essentially by two effects: calendrical aging of the battery, and cyclic aging of the battery. Calendrical aging of the battery is greatly influenced by the average state of charge (SOC). Cyclic aging of the battery is based on the regular charging and discharging of the battery. An essential determining variable for cyclic aging is the depth of discharge (DOD).
A battery may be configured so that a specific service life is achieved in the context of an average depth of discharge or a characteristic charging and discharging profile. The “service life” is defined, for example, as the time at which the battery has lost 20% of its original (energy storage) capacity. Certain safety margins are often also implemented, intended to ensure that the service life is in fact attained.
Aging models that characterize aging of the battery are used in connection with the service life. As a battery's age increases, its “state of health” SOH decreases. The state of health SOH is usually defined as a number between 1 (beginning of the battery's service life) and 0 (end of the battery's service life).
Patent document DE 10 2007 038 586 A1 discusses a method for service life monitoring and optimum utilization of a battery of a hybrid vehicle. Here the battery is stressed within dynamically predefined stress limits, these stress limits being calculated as a function of state and of the previous utilization of the battery. The calculation is based on a stress index that is ascertained on the basis of utilization of the battery's state of charge, the battery temperature, the battery voltage, and/or the voltage of individual cells of the battery.